diff --git a/MdePkg/Include/IndustryStandard/Acpi65.h b/MdePkg/Include/IndustryStandard/Acpi65.h
index fab613d3a7..d79d0b2b5f 100644
--- a/MdePkg/Include/IndustryStandard/Acpi65.h
+++ b/MdePkg/Include/IndustryStandard/Acpi65.h
@@ -43,6 +43,7 @@ typedef struct {
 #define EFI_ACPI_6_5_GENERAL_PURPOSE_IO              0x08
 #define EFI_ACPI_6_5_GENERIC_SERIAL_BUS              0x09
 #define EFI_ACPI_6_5_PLATFORM_COMMUNICATION_CHANNEL  0x0A
+#define EFI_ACPI_6_5_PLATFORM_RUNTIME_MECHANISM      0x0B
 #define EFI_ACPI_6_5_FUNCTIONAL_FIXED_HARDWARE       0x7F
 
 //